The invention relates to a superstructure construction comprising a rail disposed above a support layer such as a concrete sleeper and in its turn extending from a securing device such as a ribbed plate, where at least one intermediate layer with a rigidity x is disposed between the support layer and the securing device.
Bedding sleepers on ballast or resorting to designs with a ballastless track and stable, rigid sleeper mountings are known. In the latter case, the sleeper such as a concrete sleeper is placed on asphalt or concrete supporting plates or suitable troughs and then partially cast in place using a sealing compound such as concrete or asphalt.
To achieve a reduction of the structure-borne and airborne sound emitted by a rail in ballastless tracks, a construction is known where a standard rail such as S54 is placed on a cork layer inside a channel comprising concrete or steel parts. In addition, cavities are provided that are filled at the top with a polyurethane/cork mixture to reduce sound.
However, this construction has not brought the desired result, and indeed sound measurements show that there has even been a 10 dB sound increase compared with the ballast construction.
A device for mounting rails for rolling stock is known from DE 89 15 837 U1, in which a ribbed plate is disposed on an elastic intermediate layer whose thickness is at least that of the ribbed plate. The intermediate layer can here have a required elasticity thanks to certain geometrical parameters. The same applies for DE 40 11 013 A1, which relates to a tempered rail structure for high-speed tracks. It is intended here to ensure, by providing a cavity with plastic-modified adhesive mortar, that a direct transmission of heat energy or cooling energy to the rail is prevented.
According to DE 41 38 575 A1, the spring rigidity of an elastic intermediate layer can be designed dependent on the contact force.

EP 0 632 164 A1 contains the proposal to structure the bottom of an elastic intermediate layer such that under load a higher rigidity results, while the transmission of sound is to be restricted at the same time.
An elastic rail support layer with bottom compression points and all-round closed edge strip is known from DE 43 14 578 A1.
The problem underlying the present invention is to develop a superstructure construction, in particular one on a ballastless track, such that a reduction of structure-borne and airborne sound is achieved.
The problem is substantially solved in accordance with the invention in that the rigidity x of the intermediate layer is rated such that at the maximum permissible and/or presettable rail stress in the rail the intermediate layer has substantially non-elastic properties such that further bending of the rail only takes place insubstantially if at all.
In accordance with the invention, the intermediate layer is rated for the permissible or required maximum rail stress, which has the advantage that the rail itself is on a softer support, thus achieving a decoupling between the rail and the sleeper. The effect of this is a lower loading of the support point and in turn a reduction in the structure-borne sound. This can be improved by using as rails those with high moment of inertia and moment of resistance when seen over the rail central axis, for example a filled section rail, so that the rail can perform the function of a support and develop a load-bearing effect. This results in a further decoupling between rail and sleeper, whereby a further reduction is achieved of the structure-borne sound emitted by the rail when it is traversed by rolling stock.
An intermediate layer is proposed that has a low rigidity before the maximum permissible and/or presettable rail stress is reached and a high rigidity when this rail stress is reached.
It is preferably provided here that the intermediate layer has a rigidity x of xxe2x89xa625 kN/mm, preferably 4xe2x89xa6xc3x97xe2x89xa625 kN/mm, and/or that at the maximum permissible rail stress the intermediate layer has a rigidity x of xxe2x89xa735 kN/mm, in particular xxe2x89xa790 kN/mm, preferably in the vicinity of 100 kN/mm.
In accordance with the invention, it is proposed that when the intermediate layer is without load it has projections extending beyond its underside and is surrounded within the intermediate layer by a cavity (recess) on the circumferential side. The cavity has a volume Va, which is equal to a volume Vb that the respective projection has in its section projecting beyond the underside.
Thanks to the structure in accordance with the invention, the projections have the function of a supporting spring which is effective when the maximum rail stress of the rail supported by the support layer has not yet been reached. If this is then reached, the projections are forced into the support layer such that the projections are flush with the underside of the intermediate layer and at the same time fill the entire cavities (recesses). As a result, the form factor of the intermediate layer is increased such that the maximum permissible rail stress is not generally exceeded even when further forces are introduced. The intermediate layer should have a rigidity x which is in the vicinity of 100 kN/mm in particular when the cavities in the support layer are completely filled by the material of the projections.
It is provided in particular that the rail is a Vignol rail with a maximum permissible rail stress of 70 to 100 N/mm2 and that the intermediate layer has a rigidity x of approximately 4 to 16 kN/mm, provided the maximum permissible rail stress has not yet been reached.
Apart from the geometry of the rail, an embodiment of the invention provides that in particular rails are used that have a moment of inertia Ix with preferably Ixxe2x89xa73400 cm4 and a moment of resistance Wx with preferably Wxxe2x89xa7350 cm3.
In particular, a superstructure construction with ballastless track is provided in which the rail is a filled section rail with a moment of inertia Ix of 3700xe2x89xa6Ixxe2x89xa63800 cm4 and a moment of resistance Wx of 390xe2x89xa6Wxxe2x89xa6410 cm3 and a maximum required rail stress "sgr" can be generated (approx. 70xc2x14 N/mm2 for rail steel UIC Class A with 880 N/mm2 tensile strength) and the intermediate layer has a rigidity x of approximately 10xc2x12 kN/mm for filled section tracks. In the case of traffic carriers with low axle loads, rigidities lower than the previously stated value are obtained.
In an embodiment of the invention, the arrangement provides for the rail to be designed at its foot such that the latter emits sound waves with a frequency v when vibrations are excited, said waves being substantially outside a frequency range between 500 and 3000 Hz. This results in a rail foot design in respect of its vibration technology that ensures a considerable reduction of the airborne sound.
In addition, the rail can be designed without a web, which also prevents problems from unwelcome airborne sound.
If the rail has a web, the latter should be designed such that it emits sound waves with a frequency v when vibrations are excited, said waves being substantially outside a frequency range between approximately 500 and 3000 Hz.
To ensure that the rail cannot tilt due to the fact that it rests on a relatively soft intermediate layer with its securing device, an embodiment of the invention provides that the rail forms together with the securing device such as a ribbed plate a unit which has the effect of widening the rail. The securing device here can be positioned inside the intermediate layer and enclosed by the latter along its longitudinal edge.
Further details, advantages and features of the invention are shown not only in the claims and in the features they containxe2x80x94singly and/or in combinationxe2x80x94but also in the following description of preferred design examples shown in the drawing.